The epithelial mesenchymal transition (EMT) and the reverse process of a mesenchymal to epithelial transition (MET) are fundamental processes during embryonic development. The changes associated with cellular plasticity that characterize them have been implicated in disease processes including cancer and fibrosis. There are numerous demonstrations that the EMT is a mechanism that can contribute to the metastatic process (Thiery, 2002; Yang and Weinberg, 2008). The EMT can be a transient and reversible process by which tumor cells acquire motile properties that allow escape from the primary tumor followed by an MET at a distant site of metastasis (Chaffer et al., 2007).
Changes in the activities of trans-acting regulators of splicing and of a number of specific splice variants have been shown to contribute to tumorigenesis (Hu and Fu, 2007). For example the SR protein SF2/ASF was shown to be a proto-oncogene that can drive tumorigenesis through the induction of changes in splicing of several target transcripts (Karni et al., 2007). In additional, splicing-specific microarray platforms that facilitate global analysis of splicing have shown the potential to yield “splicing signatures” that can be used for cancer diagnosis and prognosis (Blencowe, 2006).
Fibroblast growth factor receptor 2 (FGFR2) is a protein that plays a role in cancer progression. The protein has two mutually exclusive exons IIIb and IIIc generated by alternative splicing events. A number of studies have demonstrated that disruption of the splicing pathway that leads to epithelial FGFR2-IIIb can contribute to cancer progression. Collective results from several models of tumorigenesis have led to the proposal that FGFR2-IIIb is a tumor suppressor (Gross et al, 2005). A general feature in such models posits that a switch from expression of FGFR2-IIIb to FGFR2-IIIc severs dependence of epithelia for growth and proliferation on surrounding mesenchyme and may establish autocrine growth pathways through epithelial expression of ligands for FGFR2-IIIc (McKeehan et al, 1998). In some cases, the switch in splicing of FGFR2 is followed by transcriptional downregulation of FGFR2 and activation of FGFR1-IIIc, which has similar ligand binding preferences as FGFR2-IIIc (Feng et al, 1997; Matsubara et al, 1998).
Reciprocal, compartment specific expression of FGFR2 splice variants and their ligands that participate in paracrine interactions between epithelial and mesenchymal cells regulate cell proliferation and differentiation (Acevedo et al. 2007). The epithelial FGFR2-IIIb splice variant has been suggested to function as a tumor suppressor (Savagner et al., 1994; Thiery, 2002). FGFR2-IIIb has a critical role in the maintenance of an epithelial phenotype. A switch in splicing towards the mesenchymal FGFR-IIIc isoform and/or transcriptional inactivation FGFR2 accompanies the EMT, a process involved in tumor metastasis (Hovhannisyan and Carstens, 2007). Previous studies of FGFR2 splicing regulation have identified a number of auxiliary cis-elements and non-cell type-specific regulatory RBPs that can influence exon IIIb and exon IIIc splicing combinatorially (Carstens et al., 1998; Hovhannisyan and Carstens, 2005) and references therein). One or more unidentified epithelial cell type-specific splicing regulatory proteins have been suggested to constitute a master switch that is required for FGFR2-IIIb expression (Newman et al., 2006).
There remains a need in the art for compositions and methods for the identification and use of splicing regulatory proteins and targets of such splicing implicated in cancer development for diagnosis/prognosis and treatment of certain cancers, as well as for use in screening assays enabling the identification of therapeutically desirable or undesirable properties of proposed therapeutic compounds or molecules.